Computer networks -- 2007-2008 -- info.uvt.ro/Course 10
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WAN communication
[edit]- connection types:
- dedicated -- synchronous serial:
- usually through leased lines;
- advantages: speed, 100% online;
- disadvantages: cost, in case of failure;
- circuit switched -- asynchronous serial:
- usually through the telephony system;
- either normal modems, ISDN or DSL;
- advantages: cost and simplicity;
- disadvantages: speed;
- packet switched -- synchronous serial:
- usually used to share the bandwidth (and costs) with other companies;
- dedicated -- synchronous serial:
DSL, ADSL, and ISDN
[edit]- DSL -- Digital Subscriber Line;
- ADSL -- Asymmetric Digital Subscriber Line;
- ISDN -- Integrated Services Digital Network:
- all work over existing phone lines;
- ISDN can be used for both voice and data (at the same time);
- links:
HDLC
[edit]- HDLC -- High Level Data Link Control:
- created by IBM as a simple data link layer protocol;
- works with synchronous serial links;
- it works at bit level;
- it has low overhead;
- it is an ISO standard;
- it doesn't support multiple network layer protocols;
- it doesn't support authentication;
- frame structure:
- flag -- 8 bits;
- address -- 8 or more bits;
- control -- 8 or 16 bits;
- data -- 0 or more bits;
- FCS -- Frame Check Sequence -- 16 or 32 bits -- a CRC;
- flag -- 8 bits;
- links:
PPP
[edit]- PPP -- Point to Point Protocol:
- it is a better version of the HDLC;
- works with both synchronous and asynchronous serial links;
- it supports multiple network layer protocols;
- it allows authentication;
- it has two sub-layers:
- LCP -- Link Control Protocol -- used for controlling the connection:
- authentication;
- compression;
- error detection;
- multilinking;
- NCP -- Network Control Protocol -- used for determining network layer parameters (like IP address);
- LCP -- Link Control Protocol -- used for controlling the connection:
- authentication:
- PAP -- Password authentication protocol:
- passwords are sent in plain text;
- the authentication is done only at the beginning of the session;
- CHAP -- Challenge Handshake authentication protocol:
- passwords are sent as salted hashes;
- authentication is done both at the beginning and during the session;
- PAP -- Password authentication protocol:
- links:
- miscellaneous:
Tunneling and VPN
[edit]- VPN -- Virtual Private Network;
- used mostly by enterprises;
- provides:
- authentication;
- encryption;
- advantages:
- security;
- disadvantages:
- processing overhead (due to encryption);
- network overhead (due to additional headers);
- there are multiple incompatible (most proprietary) standards;
- links:
Miscellaneous
[edit]- data processing:
- data access:
- data formating:
- JSON example:
{
"firstName": "John",
"lastName": "Smith",
"address": {
"streetAddress": "21 2nd Street",
"city": "New York",
"state": "NY",
"postalCode": 10021
},
"phoneNumbers": [
"212 555-1234",
"646 555-4567"
]
}
- XML example:
<recipe name="bread" prep_time="5 mins" cook_time="3 hours">
<title>Basic bread</title>
<ingredient amount="3" unit="cups">Flour</ingredient>
<ingredient amount="0.25" unit="ounce">Yeast</ingredient>
<ingredient amount="1.5" unit="cups" state="warm">Water</ingredient>
<ingredient amount="1" unit="teaspoon">Salt</ingredient>
<instructions>
<step>Mix all ingredients together.</step>
<step>Knead thoroughly.</step>
<step>Cover with a cloth, and leave for one hour in warm room.</step>
<step>Knead again.</step>
<step>Place in a bread baking tin.</step>
<step>Cover with a cloth, and leave for one hour in warm room.</step>
<step>Bake in the oven at 350(degrees)F for 30 minutes.</step>
</instructions>
</recipe>
- ASN1 definition example:
FooProtocol DEFINITIONS ::= BEGIN FooQuestion ::= SEQUENCE { trackingNumber INTEGER, question IA5String } FooAnswer ::= SEQUENCE { questionNumber INTEGER, answer BOOLEAN } END