{"id":185,"date":"2014-06-26T18:49:12","date_gmt":"2014-06-26T11:49:12","guid":{"rendered":"https:\/\/beta.engisv.info\/?p=185"},"modified":"2014-06-26T18:49:12","modified_gmt":"2014-06-26T11:49:12","slug":"mo-hinh-tham-chieu-osi-open-systems-interconnect","status":"publish","type":"post","link":"https:\/\/www.engisv.info\/?p=185","title":{"rendered":"M\u00f4 h\u00ecnh tham chi\u1ebfu OSI (Open Systems Interconnect)"},"content":{"rendered":"

\u1ede th\u1eddi k\u1ef3 \u0111\u1ea7u c\u1ee7a c\u00f4ng ngh\u1ec7 n\u1ed1i m\u1ea1ng, vi\u1ec7c g\u1eedi v\u00e0 nh\u1eadn d\u1eef li\u1ec7u ngang qua m\u1ea1ng th\u01b0\u1eddng g\u00e2y nh\u1ea7m l\u1eabn do c\u00e1c c\u00f4ng ty l\u1edbn nh\u01b0 IBM, Honeywell v\u00e0 Digital Equipment Corporation t\u1ef1 \u0111\u1ec1 ra nh\u1eefng ti\u00eau chu\u1ea9n ri\u00eang cho ho\u1ea1t \u0111\u1ed9ng k\u1ebft n\u1ed1i m\u00e1y t\u00ednh.<\/p>\n

N\u0103m 1984, t\u1ed5 ch\u1ee9c Ti\u00eau chu\u1ea9n ho\u00e1 Qu\u1ed1c t\u1ebf – ISO (International Standard Organization) ch\u00ednh th\u1ee9c \u0111\u01b0a ra m\u00f4 h\u00ecnh OSI (Open Systems Interconnection), l\u00e0 t\u1eadp h\u1ee3p c\u00e1c \u0111\u1eb7c \u0111i\u1ec3m k\u1ef9 thu\u1eadt m\u00f4 t\u1ea3 ki\u1ebfn tr\u00fac m\u1ea1ng d\u00e0nh cho vi\u1ec7c k\u1ebft n\u1ed1i c\u00e1c thi\u1ebft b\u1ecb kh\u00f4ng c\u00f9ng ch\u1ee7ng lo\u1ea1i.<\/p>\n

M\u00f4 h\u00ecnh OSI \u0111\u01b0\u1ee3c chia th\u00e0nh 7 t\u1ea7ng, m\u1ed7i t\u1ea7ng bao g\u1ed3m nh\u1eefng ho\u1ea1t \u0111\u1ed9ng, thi\u1ebft b\u1ecb v\u00e0 giao th\u1ee9c m\u1ea1ng kh\u00e1c nhau.
\n\"\"<\/p>\n

C\u00e1c giao th\u1ee9c trong m\u00f4 h\u00ecnh OSI:<\/strong>
\nTrong m\u00f4 h\u00ecnh OSI c\u00f3 hai lo\u1ea1i giao th\u1ee9c ch\u00ednh \u0111\u01b0\u1ee3c \u00e1p d\u1ee5ng: giao th\u1ee9c c\u00f3 li\u00ean k\u1ebft (connection – oriented) v\u00e0 giao th\u1ee9c kh\u00f4ng li\u00ean k\u1ebft (connectionless).<\/p>\n

\u2212 Giao th\u1ee9c c\u00f3 li\u00ean k\u1ebft: tr\u01b0\u1edbc khi truy\u1ec1n d\u1eef li\u1ec7u hai t\u1ea7ng \u0111\u1ed3ng m\u1ee9c c\u1ea7n thi\u1ebft l\u1eadp m\u1ed9t li\u00ean k\u1ebft logic v\u00e0 c\u00e1c g\u00f3i tin \u0111\u01b0\u1ee3c trao \u0111\u1ed5i th\u00f4ng qua li\u00ean k\u1ebft n\u00e1y, vi\u1ec7c c\u00f3 li\u00ean k\u1ebft logic s\u1ebd n\u00e2ng cao \u0111\u1ed9 an to\u00e0n trong truy\u1ec1n d\u1eef li\u1ec7u.<\/p>\n

\u2212 Giao th\u1ee9c kh\u00f4ng li\u00ean k\u1ebft: tr\u01b0\u1edbc khi truy\u1ec1n d\u1eef li\u1ec7u kh\u00f4ng thi\u1ebft l\u1eadp li\u00ean k\u1ebft logic v\u00e0 m\u1ed7i g\u00f3i tin \u0111\u01b0\u1ee3c truy\u1ec1n \u0111\u1ed9c l\u1eadp v\u1edbi c\u00e1c g\u00f3i tin tr\u01b0\u1edbc ho\u1eb7c sau n\u00f3. Nh\u01b0 v\u1eady v\u1edbi giao th\u1ee9c c\u00f3 li\u00ean k\u1ebft, qu\u00e1 tr\u00ecnh truy\u1ec1n th\u00f4ng ph\u1ea3i g\u1ed3m 3 giai \u0111o\u1ea1n ph\u00e2n bi\u1ec7t:<\/p>\n

\u2212 Thi\u1ebft l\u1eadp li\u00ean k\u1ebft (logic): hai th\u1ef1c th\u1ec3 \u0111\u1ed3ng m\u1ee9c \u1edf hai h\u1ec7 th\u1ed1ng th\u01b0\u01a1ng l\u01b0\u1ee3ng v\u1edbi nhau v\u1ec1 t\u1eadp c\u00e1c tham s\u1ed1 s\u1ebd s\u1eed d\u1ee5ng trong giai \u0111o\u1ea1n sau (truy\u1ec1n d\u1eef li\u1ec7u).<\/p>\n

\u2212 Truy\u1ec1n d\u1eef li\u1ec7u: d\u1eef li\u1ec7u \u0111\u01b0\u1ee3c truy\u1ec1n v\u1edbi c\u00e1c c\u01a1 ch\u1ebf ki\u1ec3m so\u00e1t v\u00e0 qu\u1ea3n l\u00fd k\u00e8m theo (nh\u01b0 ki\u1ec3m so\u00e1t l\u1ed7i, ki\u1ec3m so\u00e1t lu\u1ed3ng d\u1eef li\u1ec7u, c\u1eaft\/h\u1ee3p d\u1eef li\u1ec7u…) \u0111\u1ec3 t\u0103ng c\u01b0\u1eddng \u0111\u1ed9 tin c\u1eady v\u00e0 hi\u1ec7u qu\u1ea3 c\u1ee7a vi\u1ec7c truy\u1ec1n d\u1eef li\u1ec7u.<\/p>\n

\u2212 H\u1ee7y b\u1ecf li\u00ean k\u1ebft (logic): gi\u1ea3i ph\u00f3ng t\u00e0i nguy\u00ean h\u1ec7 th\u1ed1ng \u0111\u00e3 \u0111\u01b0\u1ee3c c\u1ea5p ph\u00e1t cho li\u00ean k\u1ebft \u0111\u1ec3 d\u00f9ng cho li\u00ean k\u1ebft kh\u00e1c.<\/p>\n

\u0110\u1ed1i v\u1edbi giao th\u1ee9c kh\u00f4ng li\u00ean k\u1ebft th\u00ec ch\u1ec9 c\u00f3 duy nh\u1ea5t m\u1ed9t giai \u0111o\u1ea1n truy\u1ec1n d\u1eef li\u1ec7u m\u00e0 th\u00f4i.
\nG\u00f3i tin c\u1ee7a giao th\u1ee9c: G\u00f3i tin (Packet) \u0111\u01b0\u1ee3c hi\u1ec3u nh\u01b0 l\u00e0 m\u1ed9t \u0111\u01a1n v\u1ecb th\u00f4ng tin d\u00f9ng trong vi\u1ec7c li\u00ean l\u1ea1c, chuy\u1ec3n giao d\u1eef li\u1ec7u trong m\u1ea1ng m\u00e1y t\u00ednh. Nh\u1eefng th\u00f4ng \u0111i\u1ec7p (message) trao \u0111\u1ed5i gi\u1eefa c\u00e1c m\u00e1y t\u00ednh trong m\u1ea1ng, \u0111\u01b0\u1ee3c t\u1ea1o d\u1ea1ng th\u00e0nh c\u00e1c g\u00f3i tin \u1edf m\u00e1y ngu\u1ed3n. V\u00e0 nh\u1eefng g\u00f3i tin n\u00e0y khi \u0111\u00edch s\u1ebd \u0111\u01b0\u1ee3c k\u1ebft h\u1ee3p l\u1ea1i th\u00e0nh th\u00f4ng \u0111i\u1ec7p ban \u0111\u1ea7u. M\u1ed9t g\u00f3i tin c\u00f3 th\u1ec3 ch\u1ee9a \u0111\u1ef1ng c\u00e1c y\u00eau c\u1ea7u ph\u1ee5c v\u1ee5, c\u00e1c th\u00f4ng tin \u0111i\u1ec1u khi\u1ec3n d\u1eed li\u1ec7u.<\/p>\n

Tr\u00ean quan \u0111i\u1ec3m m\u00f4 h\u00ecnh m\u1ea1ng ph\u00e2n t\u1ea7ng t\u1ea7ng m\u1ed7i t\u1ea7ng ch\u1ec9 th\u1ef1c hi\u1ec7n m\u1ed9t ch\u1ee9c n\u0103ng l\u00e0 nh\u1eadn d\u1eef li\u1ec7u t\u1eeb t\u1ea7ng b\u00ean tr\u00ean \u0111\u1ec3 chuy\u1ec3n giao xu\u1ed1ng cho t\u1ea7ng b\u00ean d\u01b0\u1edbi v\u00e0 ng\u01b0\u1ee3c l\u1ea1i. Ch\u1ee9c n\u0103ng n\u00e0y th\u1ef1c ch\u1ea5t l\u00e0 g\u1eafn th\u00eam v\u00e0 g\u1ee1 b\u1ecf ph\u1ea7n \u0111\u1ea7u (header) \u0111\u1ed1i v\u1edbi c\u00e1c g\u00f3i tin tr\u01b0\u1edbc khi chuy\u1ec3n n\u00f3 \u0111i. N\u00f3i c\u00e1ch kh\u00e1c, t\u1eebng g\u00f3i tin bao g\u1ed3m ph\u1ea7n \u0111\u1ea7u (header) v\u00e0 ph\u1ea7n d\u1eef li\u1ec7u. Khi \u0111i \u0111\u1ebfn m\u1ed9t t\u1ea7ng m\u1edbi g\u00f3i tin s\u1ebd \u0111\u01b0\u1ee3c \u0111\u00f3ng th\u00eam m\u1ed9t ph\u1ea7n \u0111\u1ea7u \u0111\u1ec1 kh\u00e1c v\u00e0 \u0111\u01b0\u1ee3c xem nh\u01b0 l\u00e0 g\u00f3i tin c\u1ee7a t\u1ea7ng m\u1edbi, c\u00f4ng vi\u1ec7c tr\u00ean ti\u1ebfp di\u1ec5n cho t\u1edbi khi g\u00f3i tin \u0111\u01b0\u1ee3c truy\u1ec1n l\u00ean \u0111\u01b0\u1eddng d\u00e2y m\u1ea1ng \u0111\u1ec3 \u0111\u1ebfn b\u00ean nh\u1eadn. T\u1ea1i b\u00ean nh\u1eadn c\u00e1c g\u00f3i tin \u0111\u01b0\u1ee3c g\u1ee1 b\u1ecf ph\u1ea7n \u0111\u1ea7u tr\u00ean t\u1eebng t\u1ea7ng t\u01b0\u1edbng \u1ee9ng v\u00e0 \u0111\u00e2y c\u0169ng l\u00e0 nguy\u00ean l\u00fd c\u1ee7a b\u1ea5t c\u1ee9 m\u00f4 h\u00ecnh ph\u00e2n t\u1ea7ng n\u00e0o.<\/p>\n

C\u00e1c ch\u1ee9c n\u0103ng ch\u1ee7 y\u1ebfu c\u1ee7a c\u00e1c t\u1ea7ng c\u1ee7a m\u00f4 h\u00ecnh OSI.\u00a0<\/strong><\/p>\n

T\u1ea7ng 1: T\u1ea7ng v\u1eadt l\u00fd (Physical Layer)<\/strong><\/p>\n

T\u1ea7ng v\u1eadt l\u00fd (Physical layer) l\u00e0 t\u1ea7ng d\u01b0\u1edbi c\u00f9ng c\u1ee7a m\u00f4 h\u00ecnh OSI l\u00e0. N\u00f3 m\u00f4 t\u1ea3 c\u00e1c \u0111\u1eb7c tr\u01b0ng v\u1eadt l\u00fd c\u1ee7a m\u1ea1ng: C\u00e1c lo\u1ea1i c\u00e1p \u0111\u01b0\u1ee3c d\u00f9ng \u0111\u1ec3 n\u1ed1i c\u00e1c thi\u1ebft b\u1ecb, c\u00e1c lo\u1ea1i \u0111\u1ea7u n\u1ed1i \u0111\u01b0\u1ee3c d\u00f9ng , c\u00e1c d\u00e2y c\u00e1p c\u00f3 th\u1ec3 d\u00e0i bao nhi\u00eau v.v… M\u1eb7t kh\u00e1c c\u00e1c t\u1ea7ng v\u1eadt l\u00fd cung c\u1ea5p c\u00e1c \u0111\u1eb7c tr\u01b0ng \u0111i\u1ec7n c\u1ee7a c\u00e1c t\u00edn hi\u1ec7u \u0111\u01b0\u1ee3c d\u00f9ng \u0111\u1ec3 khi chuy\u1ec3n d\u1eef li\u1ec7u tr\u00ean c\u00e1p t\u1eeb m\u1ed9t m\u00e1y n\u00e0y \u0111\u1ebfn m\u1ed9t m\u00e1y kh\u00e1c c\u1ee7a m\u1ea1ng, k\u1ef9 thu\u1eadt n\u1ed1i m\u1ea1ch \u0111i\u1ec7n, t\u1ed1c \u0111\u1ed9 c\u00e1p truy\u1ec1n d\u1eabn.<\/p>\n

T\u1ea7ng v\u1eadt l\u00fd kh\u00f4ng qui \u0111\u1ecbnh m\u1ed9t \u00fd ngh\u0129a n\u00e0o cho c\u00e1c t\u00edn hi\u1ec7u \u0111\u00f3 ngo\u00e0i c\u00e1c gi\u00e1 tr\u1ecb nh\u1ecb ph\u00e2n 0 v\u00e0 1. \u1ede c\u00e1c t\u1ea7ng cao h\u01a1n c\u1ee7a m\u00f4 h\u00ecnh OSI \u00fd ngh\u0129a c\u1ee7a c\u00e1c bit \u0111\u01b0\u1ee3c truy\u1ec1n \u1edf t\u1ea7ng v\u1eadt l\u00fd s\u1ebd \u0111\u01b0\u1ee3c x\u00e1c \u0111\u1ecbnh.
\nV\u00ed d\u1ee5: Ti\u00eau chu\u1ea9n Ethernet cho c\u00e1p xo\u1eafn \u0111\u00f4i 10 baseT \u0111\u1ecbnh r\u00f5 c\u00e1c \u0111\u1eb7c tr\u01b0ng \u0111i\u1ec7n c\u1ee7a c\u00e1p xo\u1eafn \u0111\u00f4i, k\u00edch th\u01b0\u1edbc v\u00e0 d\u1ea1ng c\u1ee7a c\u00e1c \u0111\u1ea7u n\u1ed1i, \u0111\u1ed9 d\u00e0i t\u1ed1i \u0111a c\u1ee7a c\u00e1p.<\/p>\n

Kh\u00e1c v\u1edbi c\u00e1c t\u1ea7ng kh\u00e1c, t\u1ea7ng v\u1eadt l\u00fd l\u00e0 kh\u00f4ng c\u00f3 g\u00f3i tin ri\u00eang v\u00e0 do v\u1eady kh\u00f4ng c\u00f3 ph\u1ea7n \u0111\u1ea7u (header) ch\u1ee9a th\u00f4ng tin \u0111i\u1ec1u khi\u1ec3n, d\u1eef li\u1ec7u \u0111\u01b0\u1ee3c truy\u1ec1n \u0111i theo d\u00f2ng bit. M\u1ed9t giao th\u1ee9c t\u1ea7ng v\u1eadt l\u00fd t\u1ed3n t\u1ea1i gi\u1eefa c\u00e1c t\u1ea7ng v\u1eadt l\u00fd \u0111\u1ec3 quy \u0111\u1ecbnh v\u1ec1 ph\u01b0\u01a1ng th\u1ee9c truy\u1ec1n (\u0111\u1ed3ng b\u1ed9, phi \u0111\u1ed3ng b\u1ed9), t\u1ed1c \u0111\u1ed9 truy\u1ec1n.<\/p>\n

T\u1ea7ng 2: T\u1ea7ng li\u00ean k\u1ebft d\u1eef li\u1ec7u (Data Link Layer)<\/strong><\/p>\n

T\u1ea7ng li\u00ean k\u1ebft d\u1eef li\u1ec7u (data link layer) l\u00e0 t\u1ea7ng m\u00e0 \u1edf \u0111\u00f3 \u00fd ngh\u0129a \u0111\u01b0\u1ee3c g\u00e1n cho c\u00e1c bit \u0111\u01b0\u1ee3c truy\u1ec1n tr\u00ean m\u1ea1ng. T\u1ea7ng li\u00ean k\u1ebft d\u1eef li\u1ec7u ph\u1ea3i quy \u0111\u1ecbnh \u0111\u01b0\u1ee3c c\u00e1c d\u1ea1ng th\u1ee9c, k\u00edch th\u01b0\u1edbc, \u0111\u1ecba ch\u1ec9 m\u00e1y g\u1eedi v\u00e0 nh\u1eadn c\u1ee7a m\u1ed7i g\u00f3i tin \u0111\u01b0\u1ee3c g\u1eedi \u0111i. N\u00f3 ph\u1ea3i x\u00e1c \u0111\u1ecbnh c\u01a1 ch\u1ebf truy nh\u1eadp th\u00f4ng tin tr\u00ean m\u1ea1ng v\u00e0 ph\u01b0\u01a1ng ti\u1ec7n g\u1eedi m\u1ed7i g\u00f3i tin sao cho n\u00f3 \u0111\u01b0\u1ee3c \u0111\u01b0a \u0111\u1ebfn cho ng\u01b0\u1eddi nh\u1eadn \u0111\u00e3 \u0111\u1ecbnh.<\/p>\n

T\u1ea7ng li\u00ean k\u1ebft d\u1eef li\u1ec7u c\u00f3 hai ph\u01b0\u01a1ng th\u1ee9c li\u00ean k\u1ebft d\u1ef1a tr\u00ean c\u00e1ch k\u1ebft n\u1ed1i c\u00e1c m\u00e1y t\u00ednh, \u0111\u00f3 l\u00e0 ph\u01b0\u01a1ng th\u1ee9c “Point-to-Point” v\u00e0 ph\u01b0\u01a1ng th\u1ee9c “Node-to-node data transfer”.<\/p>\n

T\u1ea7ng li\u00ean k\u1ebft d\u1eef li\u1ec7u c\u0169ng cung c\u1ea5p c\u00e1ch ph\u00e1t hi\u1ec7n v\u00e0 s\u1eeda l\u1ed7i c\u01a1 b\u1ea3n \u0111\u1ec3 \u0111\u1ea3m b\u1ea3o cho d\u1eef li\u1ec7u nh\u1eadn \u0111\u01b0\u1ee3c gi\u1ed1ng ho\u00e0n to\u00e0n v\u1edbi d\u1eef li\u1ec7u g\u1eedi \u0111i. N\u1ebfu m\u1ed9t g\u00f3i tin c\u00f3 l\u1ed7i kh\u00f4ng s\u1eeda \u0111\u01b0\u1ee3c, t\u1ea7ng li\u00ean k\u1ebft d\u1eef li\u1ec7u ph\u1ea3i ch\u1ec9 ra \u0111\u01b0\u1ee3c c\u00e1ch th\u00f4ng b\u00e1o cho n\u01a1i g\u1eedi bi\u1ebft g\u00f3i tin \u0111\u00f3 c\u00f3 l\u1ed7i \u0111\u1ec3 n\u00f3 g\u1eedi l\u1ea1i.<\/p>\n

C\u00e1c giao th\u1ee9c t\u1ea7ng li\u00ean k\u1ebft d\u1eef li\u1ec7u chia l\u00e0m 2 lo\u1ea1i ch\u00ednh l\u00e0 c\u00e1c giao th\u1ee9c h\u01b0\u1edbng k\u00fd t\u01b0 v\u00e0 c\u00e1c giao th\u1ee9c h\u01b0\u1edbng bit. C\u00e1c giao th\u1ee9c h\u01b0\u1edbng k\u00fd t\u1ef1 \u0111\u01b0\u1ee3c x\u00e2y d\u1ef1ng d\u1ef1a tr\u00ean c\u00e1c k\u00fd t\u1ef1 \u0111\u1eb7c bi\u1ec7t c\u1ee7a m\u1ed9t b\u1ed9 m\u00e3 chu\u1ea9n n\u00e0o \u0111\u00f3 (nh\u01b0 ASCII hay EBCDIC), trong khi \u0111\u00f3 c\u00e1c giao th\u1ee9c h\u01b0\u1edbng bit l\u1ea1i d\u00f9ng c\u00e1c c\u1ea5u tr\u00fac nh\u1ecb ph\u00e2n (x\u00e2u bit) \u0111\u1ec3 x\u00e2y d\u1ef1ng c\u00e1c ph\u1ea7n t\u1eed c\u1ee7a giao th\u1ee9c (\u0111\u01a1n v\u1ecb d\u1eef li\u1ec7u, c\u00e1c th\u1ee7 t\u1ee5c.) v\u00e0 khi nh\u1eadn, d\u1eef li\u1ec7u s\u1ebd \u0111\u01b0\u1ee3c ti\u1ebfp nh\u1eadn l\u1ea7n l\u01b0\u1ee3t t\u1eebng bit m\u1ed9t.<\/p>\n

T\u1ea7ng 3: T\u1ea7ng m\u1ea1ng (Network Layer)<\/strong><\/p>\n

T\u1ea7ng m\u1ea1ng (network layer) nh\u1eafm \u0111\u1ebfn vi\u1ec7c k\u1ebft n\u1ed1i c\u00e1c m\u1ea1ng v\u1edbi nhau b\u1eb1ng c\u00e1ch t\u00ecm \u0111\u01b0\u1eddng (routing) cho c\u00e1c g\u00f3i tin t\u1eeb m\u1ed9t m\u1ea1ng n\u00e0y \u0111\u1ebfn m\u1ed9t m\u1ea1ng kh\u00e1c. N\u00f3 x\u00e1c \u0111\u1ecbnh vi\u1ec7c chuy\u1ec3n h\u01b0\u1edbng, v\u1ea1ch \u0111\u01b0\u1eddng c\u00e1c g\u00f3i tin trong m\u1ea1ng, c\u00e1c g\u00f3i n\u00e0y c\u00f3 th\u1ec3 ph\u1ea3i \u0111i qua nhi\u1ec1u ch\u1eb7ng tr\u01b0\u1edbc khi \u0111\u1ebfn \u0111\u01b0\u1ee3c \u0111\u00edch cu\u1ed1i c\u00f9ng. N\u00f3 lu\u00f4n t\u00ecm c\u00e1c tuy\u1ebfn truy\u1ec1n th\u00f4ng kh\u00f4ng t\u1eafc ngh\u1ebdn \u0111\u1ec3 \u0111\u01b0a c\u00e1c g\u00f3i tin \u0111\u1ebfn \u0111\u00edch.<\/p>\n

T\u1ea7ng m\u1ea1ng cung c\u00e1c c\u00e1c ph\u01b0\u01a1ng ti\u1ec7n \u0111\u1ec3 truy\u1ec1n c\u00e1c g\u00f3i tin qua m\u1ea1ng, th\u1eadm ch\u00ed qua m\u1ed9t m\u1ea1ng c\u1ee7a m\u1ea1ng (network of network). B\u1edfi v\u1eady n\u00f3 c\u1ea7n ph\u1ea3i \u0111\u00e1p \u1ee9ng v\u1edbi nhi\u1ec1u ki\u1ec3u m\u1ea1ng v\u00e0 nhi\u1ec1u ki\u1ec3u d\u1ecbch v\u1ee5 cung c\u1ea5p b\u1edfi c\u00e1c m\u1ea1ng kh\u00e1c nhau. hai ch\u1ee9c n\u0103ng ch\u1ee7 y\u1ebfu c\u1ee7a t\u1ea7ng m\u1ea1ng l\u00e0 ch\u1ecdn \u0111\u01b0\u1eddng (routing) v\u00e0 chuy\u1ec3n ti\u1ebfp (relaying). T\u1ea7ng m\u1ea1ng l\u00e0 quan tr\u1ecdng nh\u1ea5t khi li\u00ean k\u1ebft hai lo\u1ea1i m\u1ea1ng kh\u00e1c nhau nh\u01b0 m\u1ea1ng Ethernet v\u1edbi m\u1ea1ng Token Ring khi \u0111\u00f3 ph\u1ea3i d\u00f9ng m\u1ed9t b\u1ed9 t\u00ecm \u0111\u01b0\u1eddng (quy \u0111\u1ecbnh b\u1edfi t\u1ea7ng m\u1ea1ng) \u0111\u1ec3 chuy\u1ec3n c\u00e1c g\u00f3i tin t\u1eeb m\u1ea1ng n\u00e0y sang m\u1ea1ng kh\u00e1c v\u00e0 ng\u01b0\u1ee3c l\u1ea1i.<\/p>\n

\u0110\u1ed1i v\u1edbi m\u1ed9t m\u1ea1ng chuy\u1ec3n m\u1ea1ch g\u00f3i (packet – switched network) – g\u1ed3m t\u1eadp h\u1ee3p c\u00e1c n\u00fat chuy\u1ec3n m\u1ea1ch g\u00f3i n\u1ed1i v\u1edbi nhau b\u1edfi c\u00e1c li\u00ean k\u1ebft d\u1eef li\u1ec7u. C\u00e1c g\u00f3i d\u1eef li\u1ec7u \u0111\u01b0\u1ee3c truy\u1ec1n t\u1eeb m\u1ed9t h\u1ec7 th\u1ed1ng m\u1edf t\u1edbi m\u1ed9t h\u1ec7 th\u1ed1ng m\u1edf kh\u00e1c tr\u00ean m\u1ea1ng ph\u1ea3i \u0111\u01b0\u1ee3c chuy\u1ec3n qua m\u1ed9t chu\u1ed7i c\u00e1c n\u00fat. M\u1ed7i n\u00fat nh\u1eadn g\u00f3i d\u1eef li\u1ec7u t\u1eeb m\u1ed9t \u0111\u01b0\u1eddng v\u00e0o (incoming link) r\u1ed3i chuy\u1ec3n ti\u1ebfp n\u00f3 t\u1edbi m\u1ed9t \u0111\u01b0\u1eddng ra (outgoing link) h\u01b0\u1edbng \u0111\u1ebfn \u0111\u00edch c\u1ee7a d\u1eef li\u1ec7u. Nh\u01b0 v\u1eady \u1edf m\u1ed7i n\u00fat trung gian n\u00f3 ph\u1ea3i th\u1ef1c hi\u1ec7n c\u00e1c ch\u1ee9c n\u0103ng ch\u1ecdn \u0111\u01b0\u1eddng v\u00e0 chuy\u1ec3n ti\u1ebfp.<\/p>\n

Vi\u1ec7c ch\u1ecdn \u0111\u01b0\u1eddng l\u00e0 s\u1ef1 l\u1ef1a ch\u1ecdn m\u1ed9t con \u0111\u01b0\u1eddng \u0111\u1ec3 truy\u1ec1n m\u1ed9t \u0111\u01a1n v\u1ecb d\u1eef li\u1ec7u (m\u1ed9t g\u00f3i tin ch\u1eb3ng h\u1ea1n) t\u1eeb tr\u1ea1m ngu\u1ed3n t\u1edbi tr\u1ea1m \u0111\u00edch c\u1ee7a n\u00f3. M\u1ed9t k\u1ef9 thu\u1eadt ch\u1ecdn \u0111\u01b0\u1eddng ph\u1ea3i th\u1ef1c hi\u1ec7n hai ch\u1ee9c n\u0103ng ch\u00ednh sau \u0111\u00e2y:<\/p>\n

\u2212 Quy\u1ebft \u0111\u1ecbnh ch\u1ecdn \u0111\u01b0\u1eddng t\u1ed1i \u01b0u d\u1ef1a tr\u00ean c\u00e1c th\u00f4ng tin \u0111\u00e3 c\u00f3 v\u1ec1 m\u1ea1ng t\u1ea1i th\u1eddi \u0111i\u1ec3m \u0111\u00f3 th\u00f4ng qua nh\u1eefng ti\u00eau chu\u1ea9n t\u1ed1i \u01b0u nh\u1ea5t \u0111\u1ecbnh.<\/p>\n

\u2212 C\u1eadp nh\u1eadt c\u00e1c th\u00f4ng tin v\u1ec1 m\u1ea1ng, t\u1ee9c l\u00e0 th\u00f4ng tin d\u00f9ng cho vi\u1ec7c ch\u1ecdn \u0111\u01b0\u1eddng, tr\u00ean m\u1ea1ng lu\u00f4n c\u00f3 s\u1ef1 thay \u0111\u1ed5i th\u01b0\u1eddng xuy\u00ean n\u00ean vi\u1ec7c c\u1eadp nh\u1eadt l\u00e0 vi\u1ec7c c\u1ea7n thi\u1ebft.<\/p>\n

Ng\u01b0\u1eddi ta c\u00f3 hai ph\u01b0\u01a1ng th\u1ee9c \u0111\u00e1p \u1ee9ng cho vi\u1ec7c ch\u1ecdn \u0111\u01b0\u1eddng l\u00e0 ph\u01b0\u01a1ng th\u1ee9c x\u1eed l\u00fd t\u1eadp trung v\u00e0 x\u1eed l\u00fd t\u1ea1i ch\u1ed7.<\/p>\n

\u2212 Ph\u01b0\u01a1ng th\u1ee9c ch\u1ecdn \u0111\u01b0\u1eddng x\u1eed l\u00fd t\u1eadp trung \u0111\u01b0\u1ee3c \u0111\u1eb7c tr\u01b0ng b\u1edfi s\u1ef1 t\u1ed3n t\u1ea1i c\u1ee7a m\u1ed9t (ho\u1eb7c v\u00e0i) trung t\u00e2m \u0111i\u1ec1u khi\u1ec3n m\u1ea1ng, ch\u00fang th\u1ef1c hi\u1ec7n vi\u1ec7c l\u1eadp ra c\u00e1c b\u1ea3ng \u0111\u01b0\u1eddng \u0111i t\u1ea1i t\u1eebng th\u1eddi \u0111i\u1ec3m cho c\u00e1c n\u00fat v\u00e0 sau \u0111\u00f3 g\u1eedi c\u00e1c b\u1ea3ng ch\u1ecdn \u0111\u01b0\u1eddng t\u1edbi t\u1eebng n\u00fat d\u1ecdc theo con \u0111\u01b0\u1eddng \u0111\u00e3 \u0111\u01b0\u1ee3c ch\u1ecdn \u0111\u00f3. Th\u00f4ng tin t\u1ed5ng th\u1ec3 c\u1ee7a m\u1ea1ng c\u1ea7n d\u00f9ng cho vi\u1ec7c ch\u1ecdn \u0111\u01b0\u1eddng ch\u1ec9 c\u1ea7n c\u1eadp nh\u1eadp v\u00e0 \u0111\u01b0\u1ee3c c\u1ea5t gi\u1eef t\u1ea1i trung t\u00e2m \u0111i\u1ec1u khi\u1ec3n m\u1ea1ng.<\/p>\n

\u2212 Ph\u01b0\u01a1ng th\u1ee9c ch\u1ecdn \u0111\u01b0\u1eddng x\u1eed l\u00fd t\u1ea1i ch\u1ed7 \u0111\u01b0\u1ee3c \u0111\u1eb7c tr\u01b0ng b\u1edfi vi\u1ec7c ch\u1ecdn \u0111\u01b0\u1eddng \u0111\u01b0\u1ee3c th\u1ef1c hi\u1ec7n t\u1ea1i m\u1ed7i n\u00fat c\u1ee7a m\u1ea1ng. Trong t\u1eebng th\u1eddi \u0111i\u1ec3m, m\u1ed7i n\u00fat ph\u1ea3i duy tr\u00ec c\u00e1c th\u00f4ng tin c\u1ee7a m\u1ea1ng v\u00e0 t\u1ef1 x\u00e2y d\u1ef1ng b\u1ea3ng ch\u1ecdn \u0111\u01b0\u1eddng cho m\u00ecnh. Nh\u01b0 v\u1eady c\u00e1c th\u00f4ng tin t\u1ed5ng th\u1ec3 c\u1ee7a m\u1ea1ng c\u1ea7n d\u00f9ng cho vi\u1ec7c ch\u1ecdn \u0111\u01b0\u1eddng c\u1ea7n c\u1eadp nh\u1eadp v\u00e0 \u0111\u01b0\u1ee3c c\u1ea5t gi\u1eef t\u1ea1i m\u1ed7i n\u00fat.<\/p>\n

Th\u00f4ng th\u01b0\u1eddng c\u00e1c th\u00f4ng tin \u0111\u01b0\u1ee3c \u0111o l\u01b0\u1eddng v\u00e0 s\u1eed d\u1ee5ng cho vi\u1ec7c ch\u1ecdn \u0111\u01b0\u1eddng bao g\u1ed3m:<\/p>\n

\u2212 Tr\u1ea1ng th\u00e1i c\u1ee7a \u0111\u01b0\u1eddng truy\u1ec1n.<\/p>\n

\u2212 Th\u1eddi gian tr\u1ec5 khi truy\u1ec1n tr\u00ean m\u1ed7i \u0111\u01b0\u1eddng d\u1eabn.<\/p>\n

\u2212 M\u1ee9c \u0111\u1ed9 l\u01b0u th\u00f4ng tr\u00ean m\u1ed7i \u0111\u01b0\u1eddng.<\/p>\n

\u2212 C\u00e1c t\u00e0i nguy\u00ean kh\u1ea3 d\u1ee5ng c\u1ee7a m\u1ea1ng.<\/p>\n

Khi c\u00f3 s\u1ef1 thay \u0111\u1ed5i tr\u00ean m\u1ea1ng (v\u00ed d\u1ee5 thay \u0111\u1ed5i v\u1ec1 c\u1ea5u tr\u00fac c\u1ee7a m\u1ea1ng do s\u1ef1 c\u1ed1 t\u1ea1i m\u1ed9t v\u00e0i n\u00fat, ph\u1ee5c h\u1ed3i c\u1ee7a m\u1ed9t n\u00fat m\u1ea1ng, n\u1ed1i th\u00eam m\u1ed9t n\u00fat m\u1edbi… ho\u1eb7c thay \u0111\u1ed5i v\u1ec1 m\u1ee9c \u0111\u1ed9 l\u01b0u th\u00f4ng) c\u00e1c th\u00f4ng tin tr\u00ean c\u1ea7n \u0111\u01b0\u1ee3c c\u1eadp nh\u1eadt v\u00e0o c\u00e1c c\u01a1 s\u1edf d\u1eef li\u1ec7u v\u1ec1 tr\u1ea1ng th\u00e1i c\u1ee7a m\u1ea1ng.<\/p>\n

T\u1ea7ng 4: T\u1ea7ng giao v\u1eadn (Transport Layer)<\/strong><\/p>\n

T\u1ea7ng v\u1eadn chuy\u1ec3n cung c\u1ea5p c\u00e1c ch\u1ee9c n\u0103ng c\u1ea7n thi\u1ebft gi\u1eefa t\u1ea7ng m\u1ea1ng v\u00e0 c\u00e1c t\u1ea7ng tr\u00ean. n\u00f3 l\u00e0 t\u1ea7ng cao nh\u1ea5t c\u00f3 li\u00ean quan \u0111\u1ebfn c\u00e1c giao th\u1ee9c trao \u0111\u1ed5i d\u1eef li\u1ec7u gi\u1eefa c\u00e1c h\u1ec7 th\u1ed1ng m\u1edf. N\u00f3 c\u00f9ng c\u00e1c t\u1ea7ng d\u01b0\u1edbi cung c\u1ea5p cho ng\u01b0\u1eddi s\u1eed d\u1ee5ng c\u00e1c ph\u1ee5c v\u1ee5 v\u1eadn chuy\u1ec3n.<\/p>\n

T\u1ea7ng v\u1eadn chuy\u1ec3n (transport layer) l\u00e0 t\u1ea7ng c\u01a1 s\u1edf m\u00e0 \u1edf \u0111\u00f3 m\u1ed9t m\u00e1y t\u00ednh c\u1ee7a m\u1ea1ng chia s\u1ebb th\u00f4ng tin v\u1edbi m\u1ed9t m\u00e1y kh\u00e1c. T\u1ea7ng v\u1eadn chuy\u1ec3n \u0111\u1ed3ng nh\u1ea5t m\u1ed7i tr\u1ea1m b\u1eb1ng m\u1ed9t \u0111\u1ecba ch\u1ec9 duy nh\u1ea5t v\u00e0 qu\u1ea3n l\u00fd s\u1ef1 k\u1ebft n\u1ed1i gi\u1eefa c\u00e1c tr\u1ea1m. T\u1ea7ng v\u1eadn chuy\u1ec3n c\u0169ng chia c\u00e1c g\u00f3i tin l\u1edbn th\u00e0nh c\u00e1c g\u00f3i tin nh\u1ecf h\u01a1n tr\u01b0\u1edbc khi g\u1eedi \u0111i. Th\u00f4ng th\u01b0\u1eddng t\u1ea7ng v\u1eadn chuy\u1ec3n \u0111\u00e1nh s\u1ed1 c\u00e1c g\u00f3i tin v\u00e0 \u0111\u1ea3m b\u1ea3o ch\u00fang chuy\u1ec3n theo \u0111\u00fang th\u1ee9 t\u1ef1.
\nT\u1ea7ng v\u1eadn chuy\u1ec3n l\u00e0 t\u1ea7ng cu\u1ed1i c\u00f9ng ch\u1ecbu tr\u00e1ch nhi\u1ec7m v\u1ec1 m\u1ee9c \u0111\u1ed9 an to\u00e0n trong truy\u1ec1n d\u1eef li\u1ec7u n\u00ean giao th\u1ee9c t\u1ea7ng v\u1eadn chuy\u1ec3n ph\u1ee5 thu\u1ed9c r\u1ea5t nhi\u1ec1u v\u00e0o b\u1ea3n ch\u1ea5t c\u1ee7a t\u1ea7ng m\u1ea1ng.<\/p>\n

T\u1ea7ng 5: T\u1ea7ng phi\u00ean (Session Layer)<\/strong><\/p>\n

T\u1ea7ng giao d\u1ecbch (session layer) thi\u1ebft l\u1eadp “c\u00e1c giao d\u1ecbch” gi\u1eefa c\u00e1c tr\u1ea1m tr\u00ean m\u1ea1ng, n\u00f3 \u0111\u1eb7t t\u00ean nh\u1ea5t qu\u00e1n cho m\u1ecdi th\u00e0nh ph\u1ea7n mu\u1ed1n \u0111\u1ed1i tho\u1ea1i v\u1edbi nhau v\u00e0 l\u1eadp \u00e1nh xa gi\u1eefa c\u00e1c t\u00ean v\u1edbi \u0111\u1ecba ch\u1ec9 c\u1ee7a ch\u00fang. M\u1ed9t giao d\u1ecbch ph\u1ea3i \u0111\u01b0\u1ee3c thi\u1ebft l\u1eadp tr\u01b0\u1edbc khi d\u1eef li\u1ec7u \u0111\u01b0\u1ee3c truy\u1ec1n tr\u00ean m\u1ea1ng, t\u1ea7ng giao d\u1ecbch \u0111\u1ea3m b\u1ea3o cho c\u00e1c giao d\u1ecbch \u0111\u01b0\u1ee3c thi\u1ebft l\u1eadp v\u00e0 duy tr\u00ec theo \u0111\u00fang qui \u0111\u1ecbnh.<\/p>\n

T\u1ea7ng giao d\u1ecbch c\u00f2n cung c\u1ea5p cho ng\u01b0\u1eddi s\u1eed d\u1ee5ng c\u00e1c ch\u1ee9c n\u0103ng c\u1ea7n thi\u1ebft \u0111\u1ec3 qu\u1ea3n tr\u1ecb c\u00e1c giao d\u1ecbnh \u1ee9ng d\u1ee5ng c\u1ee7a h\u1ecd, c\u1ee5 th\u1ec3 l\u00e0:<\/p>\n

\u2212 \u0110i\u1ec1u ph\u1ed1i vi\u1ec7c trao \u0111\u1ed5i d\u1eef li\u1ec7u gi\u1eefa c\u00e1c \u1ee9ng d\u1ee5ng b\u1eb1ng c\u00e1ch thi\u1ebft l\u1eadp v\u00e0 gi\u1ea3i ph\u00f3ng (m\u1ed9t c\u00e1ch l\u00f4gic) c\u00e1c phi\u00ean (hay c\u00f2n g\u1ecdi l\u00e0 c\u00e1c h\u1ed9i tho\u1ea1i – dialogues)<\/p>\n

\u2212 Cung c\u1ea5p c\u00e1c \u0111i\u1ec3m \u0111\u1ed3ng b\u1ed9 \u0111\u1ec3 ki\u1ec3m so\u00e1t vi\u1ec7c trao \u0111\u1ed5i d\u1eef li\u1ec7u.<\/p>\n

\u2212 \u00c1p \u0111\u1eb7t c\u00e1c qui t\u1eafc cho c\u00e1c t\u01b0\u01a1ng t\u00e1c gi\u1eefa c\u00e1c \u1ee9ng d\u1ee5ng c\u1ee7a ng\u01b0\u1eddi s\u1eed d\u1ee5ng.<\/p>\n

\u2212 Cung c\u1ea5p c\u01a1 ch\u1ebf “l\u1ea5y l\u01b0\u1ee3t” (n\u1eafm quy\u1ec1n) trong qu\u00e1 tr\u00ecnh trao \u0111\u1ed5i d\u1eef li\u1ec7u.<\/p>\n

Trong tr\u01b0\u1eddng h\u1ee3p m\u1ea1ng l\u00e0 hai chi\u1ec1u lu\u00e2n phi\u00ean th\u00ec n\u1ea9y sinh v\u1ea5n \u0111\u1ec1: hai ng\u01b0\u1eddi s\u1eed d\u1ee5ng lu\u00e2n phi\u00ean ph\u1ea3i “l\u1ea5y l\u01b0\u1ee3t” \u0111\u1ec3 truy\u1ec1n d\u1eef li\u1ec7u. T\u1ea7ng giao d\u1ecbch duy tr\u00ec t\u01b0\u01a1ng t\u00e1c lu\u00e2n phi\u00ean b\u1eb1ng c\u00e1ch b\u00e1o cho m\u1ed7i ng\u01b0\u1eddi s\u1eed d\u1ee5ng khi \u0111\u1ebfn l\u01b0\u1ee3t h\u1ecd \u0111\u01b0\u1ee3c truy\u1ec1n d\u1eef li\u1ec7u. V\u1ea5n \u0111\u1ec1 \u0111\u1ed3ng b\u1ed9 h\u00f3a trong t\u1ea7ng giao d\u1ecbch c\u0169ng \u0111\u01b0\u1ee3c th\u1ef1c hi\u1ec7n nh\u01b0 c\u01a1 ch\u1ebf ki\u1ec3m tra\/ph\u1ee5c h\u1ed3i, d\u1ecbch v\u1ee5 n\u00e0y cho ph\u00e9p ng\u01b0\u1eddi s\u1eed d\u1ee5ng x\u00e1c \u0111\u1ecbnh c\u00e1c \u0111i\u1ec3m \u0111\u1ed3ng b\u1ed9 h\u00f3a trong d\u00f2ng d\u1eef li\u1ec7u \u0111ang chuy\u1ec3n v\u1eadn v\u00e0 khi c\u1ea7n thi\u1ebft c\u00f3 th\u1ec3 kh\u00f4i ph\u1ee5c vi\u1ec7c h\u1ed9i tho\u1ea1i b\u1eaft \u0111\u1ea7u t\u1eeb m\u1ed9t trong c\u00e1c \u0111i\u1ec3m \u0111\u00f3.<\/p>\n

\u1ede m\u1ed9t th\u1eddi \u0111i\u1ec3m ch\u1ec9 c\u00f3 m\u1ed9t ng\u01b0\u1eddi s\u1eed d\u1ee5ng \u0111\u00f3 quy\u1ec1n \u0111\u1eb7c bi\u1ec7t \u0111\u01b0\u1ee3c g\u1ecdi c\u00e1c d\u1ecbch v\u1ee5 nh\u1ea5t \u0111\u1ecbnh c\u1ee7a t\u1ea7ng giao d\u1ecbch, vi\u1ec7c ph\u00e2n b\u1ed5 c\u00e1c quy\u1ec1n n\u00e0y th\u00f4ng qua trao \u0111\u1ed5i th\u1ebb b\u00e0i (token). V\u00ed d\u1ee5: Ai c\u00f3 \u0111\u01b0\u1ee3c token s\u1ebd c\u00f3 quy\u1ec1n truy\u1ec1n d\u1eef li\u1ec7u, v\u00e0 khi ng\u01b0\u1eddi gi\u1eef token trao token cho ng\u01b0\u1eddi kh\u00e1c thi c\u0169ng c\u00f3 ngh\u0129a trao quy\u1ec1n truy\u1ec1n d\u1eef li\u1ec7u cho ng\u01b0\u1eddi \u0111\u00f3.<\/p>\n

T\u1ea7ng giao d\u1ecbch c\u00f3 c\u00e1c h\u00e0m c\u01a1 b\u1ea3n sau:<\/p>\n

\u2212 Give Token cho ph\u00e9p ng\u01b0\u1eddi s\u1eed d\u1ee5ng chuy\u1ec3n m\u1ed9t token cho m\u1ed9t ng\u01b0\u1eddi s\u1eed d\u1ee5ng kh\u00e1c c\u1ee7a m\u1ed9t li\u00ean k\u1ebft giao d\u1ecbch.<\/p>\n

\u2212 Please Token cho ph\u00e9p m\u1ed9t ng\u01b0\u1eddi s\u1eed d\u1ee5ng ch\u01b0a c\u00f3 token c\u00f3 th\u1ec3 y\u00eau c\u1ea7u token \u0111\u00f3.<\/p>\n

\u2212 Give Control d\u00f9ng \u0111\u1ec3 chuy\u1ec3n t\u1ea5t c\u1ea3 c\u00e1c token t\u1eeb m\u1ed9t ng\u01b0\u1eddi s\u1eed d\u1ee5ng sang m\u1ed9t ng\u01b0\u1eddi s\u1eed d\u1ee5ng kh\u00e1c.<\/p>\n

T\u1ea7ng 6: T\u1ea7ng tr\u00ecnh di\u1ec5n (Presentation Layer)<\/strong><\/p>\n

Trong giao ti\u1ebfp gi\u1eefa c\u00e1c \u1ee9ng d\u1ee5ng th\u00f4ng qua m\u1ea1ng v\u1edbi c\u00f9ng m\u1ed9t d\u1eef li\u1ec7u c\u00f3 th\u1ec3 c\u00f3 nhi\u1ec1u c\u00e1ch bi\u1ec3u di\u1ec5n kh\u00e1c nhau. Th\u00f4ng th\u01b0\u1eddng d\u1ea1ng bi\u1ec3u di\u1ec5n d\u00f9ng b\u1edfi \u1ee9ng d\u1ee5ng ngu\u1ed3n v\u00e0 d\u1ea1ng bi\u1ec3u di\u1ec5n d\u00f9ng b\u1edfi \u1ee9ng d\u1ee5ng \u0111\u00edch c\u00f3 th\u1ec3 kh\u00e1c nhau do c\u00e1c \u1ee9ng d\u1ee5ng \u0111\u01b0\u1ee3c ch\u1ea1y tr\u00ean c\u00e1c h\u1ec7 th\u1ed1ng ho\u00e0n to\u00e0n kh\u00e1c nhau (nh\u01b0 h\u1ec7 m\u00e1y Intel v\u00e0 h\u1ec7 m\u00e1y Motorola). T\u1ea7ng th\u1ec3 hi\u1ec7n (Presentation layer) ph\u1ea3i ch\u1ecbu tr\u00e1ch nhi\u1ec7m chuy\u1ec3n \u0111\u1ed5i d\u1eef li\u1ec7u g\u1eedi \u0111i tr\u00ean m\u1ea1ng t\u1eeb m\u1ed9t lo\u1ea1i bi\u1ec3u di\u1ec5n n\u00e0y sang m\u1ed9t lo\u1ea1i kh\u00e1c. \u0110\u1ec3 \u0111\u1ea1t \u0111\u01b0\u1ee3c \u0111i\u1ec1u \u0111\u00f3 n\u00f3 cung c\u1ea5p m\u1ed9t d\u1ea1ng bi\u1ec3u di\u1ec5n chung d\u00f9ng \u0111\u1ec3 truy\u1ec1n th\u00f4ng v\u00e0 cho ph\u00e9p chuy\u1ec3n \u0111\u1ed5i t\u1eeb d\u1ea1ng bi\u1ec3u di\u1ec5n c\u1ee5c b\u1ed9 sang bi\u1ec3u di\u1ec5n chung v\u00e0 ng\u01b0\u1ee3c l\u1ea1i. T\u1ea7ng th\u1ec3 hi\u1ec7n c\u0169ng c\u00f3 th\u1ec3 \u0111\u01b0\u1ee3c d\u00f9ng k\u0129 thu\u1eadt m\u00e3 h\u00f3a \u0111\u1ec3 x\u00e1o tr\u1ed9n c\u00e1c d\u1eef li\u1ec7u tr\u01b0\u1edbc khi \u0111\u01b0\u1ee3c truy\u1ec1n \u0111i v\u00e0 gi\u1ea3i m\u00e3 \u1edf \u0111\u1ea7u \u0111\u1ebfn \u0111\u1ec3 b\u1ea3o m\u1eadt. Ngo\u00e0i ra t\u1ea7ng th\u1ec3 hi\u1ec7n c\u0169ng c\u00f3 th\u1ec3 d\u00f9ng c\u00e1c k\u0129 thu\u1eadt n\u00e9n sao cho ch\u1ec9 c\u1ea7n m\u1ed9t \u00edt byte d\u1eef li\u1ec7u \u0111\u1ec3 th\u1ec3 hi\u1ec7n th\u00f4ng tin khi n\u00f3 \u0111\u01b0\u1ee3c truy\u1ec1n \u1edf tr\u00ean m\u1ea1ng, \u1edf \u0111\u1ea7u nh\u1eadn, t\u1ea7ng tr\u00ecnh b\u00e0y bung tr\u1edf l\u1ea1i \u0111\u1ec3 \u0111\u01b0\u1ee3c d\u1eef li\u1ec7u ban \u0111\u1ea7u.<\/p>\n

T\u1ea7ng 7: T\u1ea7ng \u1ee9ng d\u1ee5ng (Application layer)<\/strong><\/p>\n

T\u1ea7ng \u1ee9ng d\u1ee5ng (Application layer) l\u00e0 t\u1ea7ng cao nh\u1ea5t c\u1ee7a m\u00f4 h\u00ecnh OSI, n\u00f3 x\u00e1c \u0111\u1ecbnh giao di\u1ec7n gi\u1eefa ng\u01b0\u1eddi s\u1eed d\u1ee5ng v\u00e0 m\u00f4i tr\u01b0\u1eddng OSI v\u00e0 gi\u1ea3i quy\u1ebft c\u00e1c k\u1ef9 thu\u1eadt m\u00e0 c\u00e1c ch\u01b0\u01a1ng tr\u00ecnh \u1ee9ng d\u1ee5ng d\u00f9ng \u0111\u1ec3 giao ti\u1ebfp v\u1edbi m\u1ea1ng.
\n\"\"M\u1ed9t s\u1ed1 \u1ee9ng d\u1ee5ng, d\u1ecbch v\u1ee5 tr\u00ean c\u00e1c t\u1ea7ng:<\/strong>
\n\"\"<\/p>\n

<\/p>\n","protected":false},"excerpt":{"rendered":"

\u1ede th\u1eddi k\u1ef3 \u0111\u1ea7u c\u1ee7a c\u00f4ng ngh\u1ec7 n\u1ed1i m\u1ea1ng, vi\u1ec7c g\u1eedi v\u00e0 nh\u1eadn d\u1eef li\u1ec7u ngang qua m\u1ea1ng th\u01b0\u1eddng g\u00e2y nh\u1ea7m l\u1eabn do c\u00e1c c\u00f4ng ty l\u1edbn nh\u01b0 IBM, Honeywell v\u00e0 Digital Equipment Corporation t\u1ef1 \u0111\u1ec1 ra nh\u1eefng ti\u00eau chu\u1ea9n ri\u00eang cho ho\u1ea1t \u0111\u1ed9ng k\u1ebft n\u1ed1i m\u00e1y t\u00ednh. N\u0103m 1984, t\u1ed5 ch\u1ee9c Ti\u00eau chu\u1ea9n ho\u00e1 Qu\u1ed1c t\u1ebf – ISO (International Standard Organization) ch\u00ednh th\u1ee9c \u0111\u01b0a ra m\u00f4 h\u00ecnh OSI (Open Systems Interconnection), l\u00e0 t\u1eadp h\u1ee3p c\u00e1c \u0111\u1eb7c \u0111i\u1ec3m k\u1ef9 thu\u1eadt m\u00f4 t\u1ea3 ki\u1ebfn tr\u00fac m\u1ea1ng d\u00e0nh cho vi\u1ec7c k\u1ebft n\u1ed1i…<\/p>\n","protected":false},"author":2,"featured_media":186,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_exactmetrics_skip_tracking":false,"footnotes":""},"categories":[7,9],"tags":[],"class_list":["post-185","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-kien-thuc","category-mang-co-ban"],"yoast_head":"\nM\u00f4 h\u00ecnh tham chi\u1ebfu OSI (Open Systems Interconnect) - EngISV<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.engisv.info\/?p=185\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"M\u00f4 h\u00ecnh tham chi\u1ebfu OSI (Open Systems Interconnect) - EngISV\" \/>\n<meta property=\"og:description\" content=\"\u1ede th\u1eddi k\u1ef3 \u0111\u1ea7u c\u1ee7a c\u00f4ng ngh\u1ec7 n\u1ed1i m\u1ea1ng, vi\u1ec7c g\u1eedi v\u00e0 nh\u1eadn d\u1eef li\u1ec7u ngang qua m\u1ea1ng th\u01b0\u1eddng g\u00e2y nh\u1ea7m l\u1eabn do c\u00e1c c\u00f4ng ty l\u1edbn nh\u01b0 IBM, Honeywell v\u00e0 Digital Equipment Corporation t\u1ef1 \u0111\u1ec1 ra nh\u1eefng ti\u00eau chu\u1ea9n ri\u00eang cho ho\u1ea1t \u0111\u1ed9ng k\u1ebft n\u1ed1i m\u00e1y t\u00ednh. N\u0103m 1984, t\u1ed5 ch\u1ee9c Ti\u00eau chu\u1ea9n ho\u00e1 Qu\u1ed1c t\u1ebf – ISO (International Standard Organization) ch\u00ednh th\u1ee9c \u0111\u01b0a ra m\u00f4 h\u00ecnh OSI (Open Systems Interconnection), l\u00e0 t\u1eadp h\u1ee3p c\u00e1c \u0111\u1eb7c \u0111i\u1ec3m k\u1ef9 thu\u1eadt m\u00f4 t\u1ea3 ki\u1ebfn tr\u00fac m\u1ea1ng d\u00e0nh cho vi\u1ec7c k\u1ebft n\u1ed1i…\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.engisv.info\/?p=185\" \/>\n<meta property=\"og:site_name\" content=\"EngISV\" \/>\n<meta property=\"article:publisher\" content=\"https:\/\/www.facebook.com\/engisv\" \/>\n<meta property=\"article:published_time\" content=\"2014-06-26T11:49:12+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/www.engisv.info\/wp-content\/uploads\/2016\/09\/osi-1-1.png\" \/>\n\t<meta property=\"og:image:width\" content=\"404\" \/>\n\t<meta property=\"og:image:height\" content=\"467\" \/>\n\t<meta property=\"og:image:type\" content=\"image\/png\" \/>\n<meta name=\"author\" content=\"hoanghiepktv\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"hoanghiepktv\" \/>\n\t<meta name=\"twitter:label2\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"21 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\\\/\\\/schema.org\",\"@graph\":[{\"@type\":\"Article\",\"@id\":\"https:\\\/\\\/www.engisv.info\\\/?p=185#article\",\"isPartOf\":{\"@id\":\"https:\\\/\\\/www.engisv.info\\\/?p=185\"},\"author\":{\"name\":\"hoanghiepktv\",\"@id\":\"https:\\\/\\\/www.engisv.info\\\/#\\\/schema\\\/person\\\/dcbab2ddc35f4c71f45c7e13f36367bf\"},\"headline\":\"M\u00f4 h\u00ecnh tham chi\u1ebfu OSI (Open Systems Interconnect)\",\"datePublished\":\"2014-06-26T11:49:12+00:00\",\"mainEntityOfPage\":{\"@id\":\"https:\\\/\\\/www.engisv.info\\\/?p=185\"},\"wordCount\":4294,\"publisher\":{\"@id\":\"https:\\\/\\\/www.engisv.info\\\/#organization\"},\"image\":{\"@id\":\"https:\\\/\\\/www.engisv.info\\\/?p=185#primaryimage\"},\"thumbnailUrl\":\"https:\\\/\\\/www.engisv.info\\\/wp-content\\\/uploads\\\/2016\\\/09\\\/osi-1-1.png\",\"articleSection\":[\"Ki\u1ebfn th\u1ee9c\",\"M\u1ea1ng c\u01a1 b\u1ea3n\"],\"inLanguage\":\"en-US\"},{\"@type\":\"WebPage\",\"@id\":\"https:\\\/\\\/www.engisv.info\\\/?p=185\",\"url\":\"https:\\\/\\\/www.engisv.info\\\/?p=185\",\"name\":\"M\u00f4 h\u00ecnh tham chi\u1ebfu OSI (Open Systems Interconnect) - EngISV\",\"isPartOf\":{\"@id\":\"https:\\\/\\\/www.engisv.info\\\/#website\"},\"primaryImageOfPage\":{\"@id\":\"https:\\\/\\\/www.engisv.info\\\/?p=185#primaryimage\"},\"image\":{\"@id\":\"https:\\\/\\\/www.engisv.info\\\/?p=185#primaryimage\"},\"thumbnailUrl\":\"https:\\\/\\\/www.engisv.info\\\/wp-content\\\/uploads\\\/2016\\\/09\\\/osi-1-1.png\",\"datePublished\":\"2014-06-26T11:49:12+00:00\",\"breadcrumb\":{\"@id\":\"https:\\\/\\\/www.engisv.info\\\/?p=185#breadcrumb\"},\"inLanguage\":\"en-US\",\"potentialAction\":[{\"@type\":\"ReadAction\",\"target\":[\"https:\\\/\\\/www.engisv.info\\\/?p=185\"]}]},{\"@type\":\"ImageObject\",\"inLanguage\":\"en-US\",\"@id\":\"https:\\\/\\\/www.engisv.info\\\/?p=185#primaryimage\",\"url\":\"https:\\\/\\\/www.engisv.info\\\/wp-content\\\/uploads\\\/2016\\\/09\\\/osi-1-1.png\",\"contentUrl\":\"https:\\\/\\\/www.engisv.info\\\/wp-content\\\/uploads\\\/2016\\\/09\\\/osi-1-1.png\",\"width\":404,\"height\":467},{\"@type\":\"BreadcrumbList\",\"@id\":\"https:\\\/\\\/www.engisv.info\\\/?p=185#breadcrumb\",\"itemListElement\":[{\"@type\":\"ListItem\",\"position\":1,\"name\":\"Home\",\"item\":\"https:\\\/\\\/www.engisv.info\\\/\"},{\"@type\":\"ListItem\",\"position\":2,\"name\":\"M\u00f4 h\u00ecnh tham chi\u1ebfu OSI (Open Systems Interconnect)\"}]},{\"@type\":\"WebSite\",\"@id\":\"https:\\\/\\\/www.engisv.info\\\/#website\",\"url\":\"https:\\\/\\\/www.engisv.info\\\/\",\"name\":\"EngISV\",\"description\":\"H\u00e3y b\u1eaft \u0111\u1ea7u t\u1eeb nh\u1eefng vi\u1ec7c nh\u1ecf!\",\"publisher\":{\"@id\":\"https:\\\/\\\/www.engisv.info\\\/#organization\"},\"potentialAction\":[{\"@type\":\"SearchAction\",\"target\":{\"@type\":\"EntryPoint\",\"urlTemplate\":\"https:\\\/\\\/www.engisv.info\\\/?s={search_term_string}\"},\"query-input\":{\"@type\":\"PropertyValueSpecification\",\"valueRequired\":true,\"valueName\":\"search_term_string\"}}],\"inLanguage\":\"en-US\"},{\"@type\":\"Organization\",\"@id\":\"https:\\\/\\\/www.engisv.info\\\/#organization\",\"name\":\"EngISV\",\"url\":\"https:\\\/\\\/www.engisv.info\\\/\",\"logo\":{\"@type\":\"ImageObject\",\"inLanguage\":\"en-US\",\"@id\":\"https:\\\/\\\/www.engisv.info\\\/#\\\/schema\\\/logo\\\/image\\\/\",\"url\":\"https:\\\/\\\/www.engisv.info\\\/wp-content\\\/uploads\\\/2018\\\/06\\\/logo2-3-1-1.png\",\"contentUrl\":\"https:\\\/\\\/www.engisv.info\\\/wp-content\\\/uploads\\\/2018\\\/06\\\/logo2-3-1-1.png\",\"width\":200,\"height\":76,\"caption\":\"EngISV\"},\"image\":{\"@id\":\"https:\\\/\\\/www.engisv.info\\\/#\\\/schema\\\/logo\\\/image\\\/\"},\"sameAs\":[\"https:\\\/\\\/www.facebook.com\\\/engisv\"]},{\"@type\":\"Person\",\"@id\":\"https:\\\/\\\/www.engisv.info\\\/#\\\/schema\\\/person\\\/dcbab2ddc35f4c71f45c7e13f36367bf\",\"name\":\"hoanghiepktv\",\"image\":{\"@type\":\"ImageObject\",\"inLanguage\":\"en-US\",\"@id\":\"https:\\\/\\\/secure.gravatar.com\\\/avatar\\\/645a174195a58b43e64a66af9255c62adc3c73faba32dda89a76c2778e9b3172?s=96&d=mm&r=g\",\"url\":\"https:\\\/\\\/secure.gravatar.com\\\/avatar\\\/645a174195a58b43e64a66af9255c62adc3c73faba32dda89a76c2778e9b3172?s=96&d=mm&r=g\",\"contentUrl\":\"https:\\\/\\\/secure.gravatar.com\\\/avatar\\\/645a174195a58b43e64a66af9255c62adc3c73faba32dda89a76c2778e9b3172?s=96&d=mm&r=g\",\"caption\":\"hoanghiepktv\"},\"url\":\"https:\\\/\\\/www.engisv.info\\\/?author=2\"}]}<\/script>\n<!-- \/ Yoast SEO plugin. -->","yoast_head_json":{"title":"M\u00f4 h\u00ecnh tham chi\u1ebfu OSI (Open Systems Interconnect) - EngISV","robots":{"index":"index","follow":"follow","max-snippet":"max-snippet:-1","max-image-preview":"max-image-preview:large","max-video-preview":"max-video-preview:-1"},"canonical":"https:\/\/www.engisv.info\/?p=185","og_locale":"en_US","og_type":"article","og_title":"M\u00f4 h\u00ecnh tham chi\u1ebfu OSI (Open Systems Interconnect) - EngISV","og_description":"\u1ede th\u1eddi k\u1ef3 \u0111\u1ea7u c\u1ee7a c\u00f4ng ngh\u1ec7 n\u1ed1i m\u1ea1ng, vi\u1ec7c g\u1eedi v\u00e0 nh\u1eadn d\u1eef li\u1ec7u ngang qua m\u1ea1ng th\u01b0\u1eddng g\u00e2y nh\u1ea7m l\u1eabn do c\u00e1c c\u00f4ng ty l\u1edbn nh\u01b0 IBM, Honeywell v\u00e0 Digital Equipment Corporation t\u1ef1 \u0111\u1ec1 ra nh\u1eefng ti\u00eau chu\u1ea9n ri\u00eang cho ho\u1ea1t \u0111\u1ed9ng k\u1ebft n\u1ed1i m\u00e1y t\u00ednh. N\u0103m 1984, t\u1ed5 ch\u1ee9c Ti\u00eau chu\u1ea9n ho\u00e1 Qu\u1ed1c t\u1ebf – ISO (International Standard Organization) ch\u00ednh th\u1ee9c \u0111\u01b0a ra m\u00f4 h\u00ecnh OSI (Open Systems Interconnection), l\u00e0 t\u1eadp h\u1ee3p c\u00e1c \u0111\u1eb7c \u0111i\u1ec3m k\u1ef9 thu\u1eadt m\u00f4 t\u1ea3 ki\u1ebfn tr\u00fac m\u1ea1ng d\u00e0nh cho vi\u1ec7c k\u1ebft n\u1ed1i…","og_url":"https:\/\/www.engisv.info\/?p=185","og_site_name":"EngISV","article_publisher":"https:\/\/www.facebook.com\/engisv","article_published_time":"2014-06-26T11:49:12+00:00","og_image":[{"width":404,"height":467,"url":"https:\/\/www.engisv.info\/wp-content\/uploads\/2016\/09\/osi-1-1.png","type":"image\/png"}],"author":"hoanghiepktv","twitter_card":"summary_large_image","twitter_misc":{"Written by":"hoanghiepktv","Est. reading time":"21 minutes"},"schema":{"@context":"https:\/\/schema.org","@graph":[{"@type":"Article","@id":"https:\/\/www.engisv.info\/?p=185#article","isPartOf":{"@id":"https:\/\/www.engisv.info\/?p=185"},"author":{"name":"hoanghiepktv","@id":"https:\/\/www.engisv.info\/#\/schema\/person\/dcbab2ddc35f4c71f45c7e13f36367bf"},"headline":"M\u00f4 h\u00ecnh tham chi\u1ebfu OSI (Open Systems Interconnect)","datePublished":"2014-06-26T11:49:12+00:00","mainEntityOfPage":{"@id":"https:\/\/www.engisv.info\/?p=185"},"wordCount":4294,"publisher":{"@id":"https:\/\/www.engisv.info\/#organization"},"image":{"@id":"https:\/\/www.engisv.info\/?p=185#primaryimage"},"thumbnailUrl":"https:\/\/www.engisv.info\/wp-content\/uploads\/2016\/09\/osi-1-1.png","articleSection":["Ki\u1ebfn th\u1ee9c","M\u1ea1ng c\u01a1 b\u1ea3n"],"inLanguage":"en-US"},{"@type":"WebPage","@id":"https:\/\/www.engisv.info\/?p=185","url":"https:\/\/www.engisv.info\/?p=185","name":"M\u00f4 h\u00ecnh tham chi\u1ebfu OSI (Open Systems Interconnect) - EngISV","isPartOf":{"@id":"https:\/\/www.engisv.info\/#website"},"primaryImageOfPage":{"@id":"https:\/\/www.engisv.info\/?p=185#primaryimage"},"image":{"@id":"https:\/\/www.engisv.info\/?p=185#primaryimage"},"thumbnailUrl":"https:\/\/www.engisv.info\/wp-content\/uploads\/2016\/09\/osi-1-1.png","datePublished":"2014-06-26T11:49:12+00:00","breadcrumb":{"@id":"https:\/\/www.engisv.info\/?p=185#breadcrumb"},"inLanguage":"en-US","potentialAction":[{"@type":"ReadAction","target":["https:\/\/www.engisv.info\/?p=185"]}]},{"@type":"ImageObject","inLanguage":"en-US","@id":"https:\/\/www.engisv.info\/?p=185#primaryimage","url":"https:\/\/www.engisv.info\/wp-content\/uploads\/2016\/09\/osi-1-1.png","contentUrl":"https:\/\/www.engisv.info\/wp-content\/uploads\/2016\/09\/osi-1-1.png","width":404,"height":467},{"@type":"BreadcrumbList","@id":"https:\/\/www.engisv.info\/?p=185#breadcrumb","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https:\/\/www.engisv.info\/"},{"@type":"ListItem","position":2,"name":"M\u00f4 h\u00ecnh tham chi\u1ebfu OSI (Open Systems Interconnect)"}]},{"@type":"WebSite","@id":"https:\/\/www.engisv.info\/#website","url":"https:\/\/www.engisv.info\/","name":"EngISV","description":"H\u00e3y b\u1eaft \u0111\u1ea7u t\u1eeb nh\u1eefng vi\u1ec7c nh\u1ecf!","publisher":{"@id":"https:\/\/www.engisv.info\/#organization"},"potentialAction":[{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https:\/\/www.engisv.info\/?s={search_term_string}"},"query-input":{"@type":"PropertyValueSpecification","valueRequired":true,"valueName":"search_term_string"}}],"inLanguage":"en-US"},{"@type":"Organization","@id":"https:\/\/www.engisv.info\/#organization","name":"EngISV","url":"https:\/\/www.engisv.info\/","logo":{"@type":"ImageObject","inLanguage":"en-US","@id":"https:\/\/www.engisv.info\/#\/schema\/logo\/image\/","url":"https:\/\/www.engisv.info\/wp-content\/uploads\/2018\/06\/logo2-3-1-1.png","contentUrl":"https:\/\/www.engisv.info\/wp-content\/uploads\/2018\/06\/logo2-3-1-1.png","width":200,"height":76,"caption":"EngISV"},"image":{"@id":"https:\/\/www.engisv.info\/#\/schema\/logo\/image\/"},"sameAs":["https:\/\/www.facebook.com\/engisv"]},{"@type":"Person","@id":"https:\/\/www.engisv.info\/#\/schema\/person\/dcbab2ddc35f4c71f45c7e13f36367bf","name":"hoanghiepktv","image":{"@type":"ImageObject","inLanguage":"en-US","@id":"https:\/\/secure.gravatar.com\/avatar\/645a174195a58b43e64a66af9255c62adc3c73faba32dda89a76c2778e9b3172?s=96&d=mm&r=g","url":"https:\/\/secure.gravatar.com\/avatar\/645a174195a58b43e64a66af9255c62adc3c73faba32dda89a76c2778e9b3172?s=96&d=mm&r=g","contentUrl":"https:\/\/secure.gravatar.com\/avatar\/645a174195a58b43e64a66af9255c62adc3c73faba32dda89a76c2778e9b3172?s=96&d=mm&r=g","caption":"hoanghiepktv"},"url":"https:\/\/www.engisv.info\/?author=2"}]}},"_links":{"self":[{"href":"https:\/\/www.engisv.info\/index.php?rest_route=\/wp\/v2\/posts\/185","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.engisv.info\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.engisv.info\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.engisv.info\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.engisv.info\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=185"}],"version-history":[{"count":0,"href":"https:\/\/www.engisv.info\/index.php?rest_route=\/wp\/v2\/posts\/185\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.engisv.info\/index.php?rest_route=\/wp\/v2\/media\/186"}],"wp:attachment":[{"href":"https:\/\/www.engisv.info\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=185"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.engisv.info\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=185"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.engisv.info\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=185"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}