ch4 review
Terms
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- Access Link: used in ____ Relay, a packet switching svc. Connected to the ____ then to the service provider's ____ Relay ____. In point2point link, this is called a _____ line.
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Frame
router
Frame, Switch
Leased - back to back link: two ____ connected to each other in a ___ to ____ WAN. connected by a ____ cable on one ____, and a ____ cable on the other.
-
routers
point, point
DCE, router
DTE - clocking: aka ____tion. The ___/___ (known as the ____) provides clocking; the ____ (known as the ____)listen for changes in ____ and adjust accordingly to match speed.
-
synchronization
CSU/DSU (DCE)
routers (DTE)
voltage - DTE:
- data terminal equipment. Receives the clocking from DCE.
- CSU/DSU...
- channel svc unit / data svc unit. Connected to a router, then csu/dsu is connected to the telco's equip. Provides clocking if present.
- DCE...
- data communications equipment. Provides clocking source for DTE (routers). Can be the CSU/DSU, or even another router with a DCE cable connected (i.e.: a back2back serial connection).
- What is Frame Relay?
-
a Packet Switching Service protocol (aka frame switching since it operates on a lower layer, 2).
Removes the need for CSU/DSU for each connected router in the WAN.
Router connects to telco's Frame Relay Switch via an Access Link. The FRS reads the frame and knows which router to send the frame to. - Standard HDLC field looks like:
-
Flag - 1 byte
Address - 1 byte
Control - 1 byte
Data - variable bytes
FCS - 4 bytes - Cisco HDLC field looks like:
-
Flag - 1 byte
Address - 1 byte
Control - 1 byte
TYPE - 2 bytes
Data - variable bytes
FCS - 4 bytes - leased line:
- from telco, connects two routers to each other in a WAN to provide network services. Engineer can request specific speed of the line.
- packet switching:
-
Alternative to leased line. Lets routers connect to each other w/out having a CSU/DSU between every router connected in the WAN. 2 kinds of PSSs are:
Frame Relay and ATM. - PPP...
- point to point protocol. 1 of 2 protocols for point to point WANs. HDLC is the other. Difference is: PPP has 'type' field in the frame (like the Cisco proprietary HDLC field). This lets you use routers from different vendors in your WAN.
- serial cable...
- many different types; used to connect router to CSU/DSU in a WAN.
- synchronous...
- is synchronization. Trying to get all routers/equipment to run at the same speed on the WAN.
- Virtual circuit...
- a Frame Relay virtual circuit. 1 serial link connects to several other routers in the WAN.